Controlled gap seals, such as carbon controlled gap seals, are commonly used in gas turbine engines, generally to seal bearing compartments. These seals are designed to run with a few thousands of an inch of clearance between a stationary carbon element and a rotating seal runner or shaft. As the temperature of the bearing area heats and cools, the seal is designed to react to temperature variations and keep the seal clearance or gap relatively constant. This may be done by having a shrink band on the carbon element. The shrink band is a metal ring that is in a tight-fitting engagement onto the carbon element. The shrink band is heated and cooled by the surrounding air, thus controlling the expansion and contraction of the carbon element. In some transient temperature excursions, the shrink band may not be sufficiently responsive as it may not be directly exposed to surrounding air. This may cause seal rub that may eventually lead to increased leakage during steady-state running of the gas turbine engine.
Accordingly, there is a need to provide an improved thermally responsive controlled gap device.